Double hung window assemblies that open and close vertically and sliding window assemblies that open and close horizontally each have two window sashes that meet at a mid-point of the assembly when the assembly is closed. One sash typically remains stationary while the other sash moves to open the assembly. The sash that most often remains stationary, for example, the upper sash of a double hung assembly, includes as its bottom segment a rail which is commonly referred to as a "keeper" rail. The lower sash includes as its top segment a rail that is commonly referred to as a "lock" rail. When the assembly is closed, an interior wall of the keeper rail abuts an exterior wall of the lock rail. These rails are referred to collectively herein as "meeting rails."
One important feature of a window assembly is its ability to minimize air infiltration between the interior of the structure and the outside. Regardless of how tightly the meeting rails abut, air tends to flow between them. To inhibit this air flow prior known window assemblies have included interconnecting rails, which provide a labyrinth through which the air must pass.
In such assemblies, the each rail supports one of a pair of opposing flanges. When the assembly is closed, these flanges interconnect. The rails, however, must separate, to accommodate the flanges. Air flow between the rails and up to the flanges is therefore increased, and the flanges are only somewhat effective in inhibiting air flow through the separated rails.
For more protection weather-stripping gaskets may be added to either side of the flanges, to shield the interconnected flanges, as discussed in Atchison U.S. Pat. No. 4,395,847. The gaskets must be relatively thick, however, to cover the gap between the rails. Accordingly, their effectiveness in preventing air infiltration is limited. Further, these gaskets are often subjected to cleaning solvents that are used to clean the windows. These solvents tend to hasten the deterioration of the gaskets, and thus, further reduce their effectiveness.
Other prior known systems include overlapping rails, such as the system discussed in Plym U.S. Pat. No. 2,057,975. These rails are enlarged and re-shaped essentially to include opposing offsets, which overlap when the assembly is closed. These rails, like the interconnecting rails discussed above, provide a circuitous route for the air, which inhibits air flow. The enlarged rails require more material, which increases their cost of manufacture and the sash weight. These heavier sashes are more difficult: to move. i.e., to raise and lower or slide, as appropriate. Further, the window assembly that incorporates these heavier rails may require strengthening to support the sashes. In particular, a double hung assembly may require strengthening to retain the heavier sashes in an open position.